/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMeshOverlay.h
Returns true if the parent-mesh edge is a "Seam" in this overlay. If present, bIsNonIntersectingOut will be true only if this is a seam edge that does not intersect with another seam or the end of the seam.
bool IsSeamEdge ( int EdgeID, bool * bIsNonIntersectingOut ) const